Insects and other pests cost farmers billions of dollars annually in crop losses and in the expense of keeping these pests under control. The losses caused by insect pests in agricultural production environments include decrease in crop yield, reduced crop quality, and increased harvesting costs.
Cultivation methods, such as crop rotation and the application of high nitrogen levels to stimulate the growth of an adventitious root system, has partially addressed problems caused by agricultural pests. Economic demands on the utilization of farmland restrict the use of crop rotation. In addition, overwintering traits of some insects are disrupting crop rotations in some areas. Thus, chemical insecticides are relied upon most heavily to guarantee the desired level of control. Insecticides are either banded onto or incorporated into the soil.
The use of chemical insecticides has several drawbacks. Continual use of insecticides has allowed resistant insects to evolve. Situations such as extremely high populations of larvae, heavy rains, and improper calibration of insecticide application equipment can result in poor control. The use of insecticides often raises environmental concerns such as contamination of soil and of both surface and underground water supplies. The public has also become concerned about the amount of residual, synthetic chemicals which might be found on food. Working with insecticides may also pose hazards to the persons applying them. Therefore, synthetic chemical pesticides are being increasingly scrutinized, and correctly so, for their potential toxic environmental consequences. Examples of widely used synthetic chemical pesticides include the organochlorines, e.g., DDT, mirex, kepone, lindane, aldrin, chlordane, aldicarb, and dieldrin; the organophosphates, e.g., chlorpyrifos, parathion, malathion, and diazinon; and carbamates. Stringent new restrictions on the use of pesticides and the elimination of some effective pesticides from the market place could limit economical and effective options for controlling damaging and costly pests.
Because of the problems associated with the use of organic synthetic chemical pesticides, there exists a clear need to limit the use of these agents and a need to identify alternative control agents. The replacement of synthetic chemical pesticides, or combination of these agents with biological pesticides, could reduce the levels of toxic chemicals in the environment.
A biological pesticidal agent that is enjoying increasing popularity is the soil microbe Bacillus thuringiensis (B.t.). The soil microbe Bacillus thuringiensis (B.t.) is a Gram-positive, spore-forming bacterium. Most strains of B.t. do not exhibit pesticidal activity. Some B.t. strains produce, and can be characterized by, parasporal crystalline protein inclusions. These inclusions often appear microscopically as distinctively shaped crystals. Some B.t. proteins are highly toxic to pests, such as insects, and are specific in their toxic activity. Certain insecticidal B.t. proteins are associated with the inclusions. These xe2x80x9cxcex4-endotoxins,xe2x80x9d are different from exotoxins, which have a non-specific host range. Other species of Bacillus also produce pesticidal proteins.
Certain Bacillus toxin genes have been isolated and sequenced, and recombinant DNA-based products have been produced and approved for use. In addition, with the use of genetic engineering techniques, new approaches for delivering these toxins to agricultural environments are under development. These include the use of plants genetically engineered with toxin genes for insect resistance and the use of stabilized intact microbial cells as toxin delivery vehicles. Thus, isolated Bacillus toxin genes are becoming commercially valuable.
Until the last fifteen years, commercial use of B.t. pesticides has been largely restricted to targeting a narrow range of lepidopteran (caterpillar) pests. Preparations of the spores and crystals of B. thuringiensis subsp.kurstaki have been used for many years as commercial insecticides for lepidopteran pests. For example, B. thuringiensis var. kurstaki HD-1 produces a crystalline xcex4-endotoxin which is toxic to the larvae of a number of lepidopteran insects.
In recent years, however, investigators have discovered B.t. pesticides with specificities for a much broader range of pests. For example, other species of B.t., namely israelensis and morrisoni (a.k.a. tenebrionis, a.k.a. B.t. M-7, a.k.a. B.t. san diego), have been used commercially to control insects of the orders Diptera and Coleoptera, respectively. Bacillus thuringiensis var. tenebrionis has been reported to be active against two beetles in the order Coleoptera (Colorado potato beetle, Leptinotarsa decemlineata, and Agelastica alni).
More recently, new subspecies of B.t. have been identified, and genes responsible for active xcex4-endotoxin proteins have been isolated. Hxc3x6fte and Whiteley classified B.t. crystal protein genes into four major classes (Hxc3x6fte, H., H. R. Whiteley [1989] Microbiological Reviews 52(2):242-255). The classes were CryI (Lepidoptera-specific), CryII (Lepidoptera- and Diptera-specific), CryIII (Coleoptera-specific), and CryIV (Diptera-specific). The discovery of strains specifically toxic to other pests has been reported. For example, CryV and CryVI have been proposed to designate a class of toxin genes that are nematode-specific.
The 1989 nomenclature and classification scheme of Hxc3x6fte and Whiteley for crystal proteins was based on both the deduced amino acid sequence and the host range of the toxin. That system was adapted to cover 14 different types of toxin genes which were divided into five major classes. The number of sequenced Bacillus thuringiensis crystal protein genes currently stands at more than 50. A revised nomenclature scheme has been proposed which is based solely on amino acid identity (Crickmore et al. [1996] Society for Invertebrate Pathology, 29th Annual Meeting, IIIrd International Colloquium on Bacillus thuringiensis, University of Cordoba, Cordoba, Spain, Sep. 1-6, 1996, abstract). The mnemonic xe2x80x9ccryxe2x80x9d has been retained for all of the toxin genes except cytA and cytB, which remain a separate class. Roman numerals have been exchanged for Arabic numerals in the primary rank, and the parentheses in the tertiary rank have been removed. Many of the original names have been retained, with the noted exceptions, although a number have been reclassified.
Many other B.t. genes have now been identified. WO 94/21795, WO 96/10083, WO 98/44137, and Estruch, J. J. et al. (1996) PNAS 93:5389-5394 describe Vip1A(a), Vip1A(b), Vip2A(a), Vip2A(b), Vip3A(a), and Vip3A(b) toxins obtained from Bacillus microbes. Those toxins are reported to be produced during vegetative cell growth and were thus termed vegetative insecticidal proteins (VIP). Activity of these toxins against certain lepidopteran and certain coleopteran pests was reported. WO 98/18932 discloses new classes of pesticidal toxins.
Obstacles to the successful agricultural use of Bacillus toxins include the development of resistance to B.t. toxins by insects. In addition, certain insects can be refractory to the effects of Bacillus toxins. The latter includes insects such as boll weevil and black cutworm as well as adult insects of most species which heretofore have demonstrated no apparent significant sensitivity to B.t. xcex4-endotoxins. While resistance management strategies in B.t. transgene plant technology have become of great interest, there remains a great need for developing additional genes that can be expressed in plants in order to effectively control various insects.
The subject application provides new classes of toxins and genes, in addition to those described in WO 98/18932, and which are distinct from those disclosed in WO 94/21795, WO 96/10083, WO 98/44137, and Estruch et al.
The subject invention concerns materials and methods useful in the control of non-mammalian pests and, particularly, plant pests. In one embodiment, the subject invention provides novel Bacillus isolates having advantageous activity against non-mammalian pests. In a further embodiment, the subject invention provides new toxins useful for the control of non-mammalian pests. In a preferred embodiment, these pests are lepidopterans and/or coleopterans. The toxins of the subject invention include xcex4-endotoxins as well as soluble toxins which can be obtained from the supernatant of Bacillus cultures.
The subject invention further provides nucleotide sequences which encode the toxins of the subject invention. The subject invention further provides nucleotide sequences and methods useful in the identification and characterization of genes which encode pesticidal toxins.
In one embodiment, the subject invention concerns unique nucleotide sequences which are useful as hybridization probes and/or primers in PCR techniques. The primers produce characteristic gene fragments which can be used in the identification, characterization, and/or isolation of specific toxin genes. The nucleotide sequences of the subject invention encode toxins which are distinct from previously-described toxins.
In a specific embodiment, the subject invention provides new classes of toxins having advantageous pesticidal activities. These classes of toxins can be encoded by polynucleotide sequences which are characterized by their ability to hybridize with certain exemplified sequences and/or by their ability to be amplified by PCR using certain exemplified primers.
One aspect of the subject invention pertains to the identification and characterization of entirely new families of Bacillus toxins having advantageous pesticidal properties. The subject invention includes new classes of genes and toxins referred to herein as MIS-7 and MIS-8. Genes and toxins of novel WAR- and SUP-classes are also disclosed. Certain MIS-1 and MIS-2 toxins and genes are also further characterized herein.
These families of toxins, and the genes which encode them, can be characterized in terms of, for example, the size of the toxin or gene, the DNA or amino acid sequence, pesticidal activity, and/or antibody reactivity. With regard to the genes encoding the novel toxin families of the subject invention, the current disclosure provides unique hybridization probes and PCR primers which can be used to identify and characterize DNA within each of the exemplified families.
In one embodiment of the subject invention, Bacillus isolates can be cultivated under conditions resulting in high multiplication of the microbe. After treating the microbe to provide single-stranded genomic nucleic acid, the DNA can be contacted with the primers of the invention and subjected to PCR amplification. Characteristic fragments of toxin-encoding genes will be amplified by the procedure, thus identifying the presence of the toxin-encoding gene(s).
A further aspect of the subject invention is the use of the disclosed nucleotide sequences as probes to detect genes encoding Bacillus toxins which are active against pests.
Further aspects of the subject invention include the genes and isolates identified using the methods and nucleotide sequences disclosed herein. The genes thus identified encode toxins active against pests. Similarly, the isolates will have activity against these pests. In a preferred embodiment, these pests are lepidopteran or coleopteran pests.
In a preferred embodiment, the subject invention concerns plants cells transformed with at least one polynucleotide sequence of the subject invention such that the transformed plant cells express pesticidal toxins in tissues consumed by target pests. As described herein, the toxins useful according to the subject invention may be chimeric toxins produced by combining portions of multiple toxins. In addition, mixtures and/or combinations of toxins can be used according to the subject invention.
Transformation of plants with the genetic constructs disclosed herein can be accomplished using techniques well known to those skilled in the art and would typically involve modification of the gene to optimize expression of the toxin in plants.
Alternatively, the Bacillus isolates of the subject invention, or recombinant microbes expressing the toxins described herein, can be used to control pests. In this regard, the invention includes the treatment of substantially intact Bacillus cells, and/or recombinant cells containing the expressed toxins of the invention, treated to prolong the pesticidal activity when the substantially intact cells are applied to the environment of a target pest. The treated cell acts as a protective coating for the pesticidal toxin. The toxin becomes active upon ingestion by a target insect.
SEQ ID NO. 1 is a nucleotide sequence encoding a toxin from B.t. strain Javelin 1990.
SEQ ID NO. 2 is an amino acid sequence for the Javelin 1990 toxin.
SEQ ID NO. 3 is a forward primer used according to the subject invention.
SEQ ID NO. 4 is a reverse primer used according to the subject invention.
SEQ ID NO. 5 is a nucleotide sequence of a toxin gene from B.t. strain PS66D3
SEQ ID NO. 6 is an amino acid sequence from the 66D3 toxin.
SEQ ID NO. 7 is a nucleotide sequence of a MIS toxin gene from B.t. strain PS177C8.
SEQ ID NO. 8 is an amino acid sequence from the 177C8-MIS toxin.
SEQ ID NO. 9 is a nucleotide sequence of a toxin gene from B.t. strain PS177I8
SEQ ID NO. 10 is an amino acid sequence from the 177I8 toxin.
SEQ ID NO. 11 is a nucleotide sequence encoding a 177C8-WAR toxin gene from B.t. strain PS177C8.
SEQ ID NO. 12 is an amino acid sequence of a 177C8-WAR toxin from B.t. strain PS177C8.
SEQ ID NOS. 13-21 are primers used according to the subject invention.
SEQ ID NO. 22 is the reverse complement of the primer of SEQ ID NO. 14.
SEQ ID NO. 23 is the reverse complement of the primer of SEQ ID NO. 15.
SEQ ID NO. 24 is the reverse complement of the primer of SEQ ID NO. 17.
SEQ ID NO. 25 is the reverse complement of the primer of SEQ ID NO. 18.
SEQ ID NO. 26 is the reverse complement of the primer of SEQ ID NO. 19.
SEQ ID NO. 27 is the reverse complement of the primer of SEQ ID NO. 20.
SEQ ID NO. 28 is the reverse complement of the primer of SEQ ID NO. 21.
SEQ ID NO. 29 is a MIS-7 forward primer.
SEQ ID NO. 30 is a MIS-7 reverse primer.
SEQ ID NO. 31 is a MIS-8 forward primer.
SEQ ID NO. 32 is a MIS-8 reverse primer.
SEQ ID NO. 33 is a nucleotide sequence of a MIS-7 toxin gene designated 157C1-A from B.t. strain PS157C1.
SEQ ID NO. 34 is an amino acid sequence of a MIS-7 toxin designated 157C1-A from B.t. strain PS157C1.
SEQ ID NO. 35 is a nucleotide sequence of a MIS-7 toxin gene from B.t. strain PS201Z.
SEQ ID NO. 36 is a nucleotide sequence of a MIS-8 toxin gene from B.t. strain PS31F2.
SEQ ID NO. 37 is a nucleotide sequence of a MIS-8 toxin gene from B.t. strain PS185Y2.
SEQ ID NO. 38 is a nucleotide sequence of a MIS-1 toxin gene from B.t. strain PS33F1.
SEQ ID NO. 39 is a MIS primer for use according to the subject invention.
SEQ ID NO. 40 is a MIS primer for use according to the subject invention.
SEQ ID NO. 41 is a WAR primer for use according to the subject invention.
SEQ ID NO. 42 is a WAR primer for use according to the subject invention.
SEQ ID NO. 43 is a partial nucleotide sequence for a MIS-7 gene from PS205C.
SEQ ID NO. 44 is a partial amino acid sequence for a MIS-7 toxin from PS205C.
SEQ ID NO. 45 is a partial nucleotide sequence for a WAR gene from PS205C.
SEQ ID NO. 46 is a partial amino acid sequence for a WAR toxin from PS205C.
SEQ ID NO. 47 is a nucleotide sequence for a MIS-8 gene from PS31F2.
SEQ ID NO. 48 is an amino acid sequence for a MIS-8 toxin from PS31F2.
SEQ ID NO. 49 is a nucleotide sequence for a WAR gene from PS31F2.
SEQ ID NO. 50 is an amino acid sequence for a WAR toxin from PS31F2.
SEQ ID NO. 51 is a SUP primer for use according to the subject invention.
SEQ ID NO. 52 is a SUP primer for use according to the subject invention.
SEQ ID NO. 53 is a nucleotide sequence for a SUP gene from KB59A4-6.
SEQ ID NO. 54 is an amino acid sequence for a SUP toxin from KB59A4-6.
The subject invention concerns materials and methods for the control of non-mammalian pests. In specific embodiments, the subject invention pertains to new Bacillus thuringiensis isolates and toxins which have activity against lepidopterans and/or coleopterans. The subject invention further concerns novel genes which encode pesticidal toxins and novel methods for identifying and characterizing Bacillus genes which encode toxins with useful properties. The subject invention concerns not only the polynucleotide sequences which encode these toxins, but also the use of these polynucleotide sequences to produce recombinant hosts which express the toxins. The proteins of the subject invention are distinct from protein toxins which have previously been isolated from Bacillus thuringiensis. 
B.t. isolates useful according to the subject invention have been deposited in the permanent collection of the Agricultural Research Service Patent Culture Collection (NRRL), Northern Regional Research Center, 1815 North University Street, Peoria, Ill. 61604, USA. The culture repository numbers of the B.t. strains are as follows:
Cultures which have been deposited for the purposes of this patent application were deposited under conditions that assure that access to the cultures is available during the pendency of this patent application to one determined by the Commissioner of Patents and Trademarks to be entitled thereto under 37 CFR 1.14 and 35 U.S.C. 122. The deposits will be available as required by foreign patent laws in countries wherein counterparts of the subject application, or its progeny, are filed. However, it should be understood that the availability of a deposit does not constitute a license to practice the subject invention in derogation of patent rights granted by governmental action.
Further, the subject culture deposits will be stored and made available to the public in accord with the provisions of the Budapest Treaty for the Deposit of Microorganisms, i.e., they will be stored with all the care necessary to keep them viable and uncontaminated for a period of at least five years after the most recent request for the furnishing of a sample of the deposit, and in any case, for a period of at least thirty (30) years after the date of deposit or for the enforceable life of any patent which may issue disclosing the culture(s). The depositor acknowledges the duty to replace the deposit(s) should the depository be unable to furnish a sample when requested, due to the condition of a deposit. All restrictions on the availability to the public of the subject culture deposits will be irrevocably removed upon the granting of a patent disclosing them.
Many of the strains useful according to the subject invention are readily available by virtue of the issuance of patents disclosing these strains or by their deposit in public collections or by their inclusion in commercial products. For example, the B.t. strain used in the commercial product, Javelin, and the HD isolates are all publicly available.
Mutants of the isolates referred to herein can be made by procedures well known in the art. For example, an asporogenous mutant can be obtained through ethylmethane sulfonate (EMS) mutagenesis of an isolate. The mutants can be made using ultraviolet light and nitrosoguanidine by procedures well known in the art.
In one embodiment, the subject invention concerns materials and methods including nucleotide primers and probes for isolating, characterizing, and identifying Bacillus genes encoding protein toxins which are active against non-mammalian pests. The nucleotide sequences described herein can also be used to identify new pesticidal Bacillus isolates. The invention further concerns the genes, isolates, and toxins identified using the methods and materials disclosed herein.
The new toxins and polynucleotide sequences provided here are defined according to several parameters. One characteristic of the toxins described herein is pesticidal activity. In a specific embodiment, these toxins have activity against coleopteran and/or lepidopteran pests. The toxins and genes of the subject invention can be further defined by their amino acid and nucleotide sequences. The sequences of the molecules can be defined in terms of homology to certain exemplified sequences as well as in terms of the ability to hybridize with, or be amplified by, certain exemplified probes and primers. The toxins provided herein can also be identified based on their immunoreactivity with certain antibodies.
An important aspect of the subject invention is the identification and characterization of new families of Bacillus toxins, and genes which encode these toxins. These families have been designated MIS-7 and MIS-8. New WAR- and SUP-type toxin families are also disclosed herein. Toxins within these families, as well as genes encoding toxins within these families, can readily be identified as described herein by, for example, size, amino acid or DNA sequence, and antibody reactivity. Amino acid and DNA sequence characteristics include homology with exemplified sequences, ability to hybridize with DNA probes, and ability to be amplified with specific primers.
A gene and toxin (which are obtainable from PS33F1) of the MIS-1 family and a gene and toxin (which are obtainable from PS66D3) of the MIS-2 family are also further characterized herein.
A novel family of toxins identified herein is the MIS-7 family. This family includes toxins which can be obtained from B.t. isolates PS157C1, PS205C, and PS201Z. The subject invention further provides probes and primers for identification of the MIS-7 genes and toxins.
A further, novel family of toxins identified herein is the MIS-8 family. This family includes toxins which can be obtained from B.t. isolates PS31F2 and PS185Y2. The subject invention further provides probes and primers for identification of the MIS-8 genes and toxins.
In a preferred embodiment, the genes of the MIS family encode toxins having a molecular weight of about 70 to about 100 kDa and, most preferably, the toxins have a size of about 80 kDa. Typically, these toxins are soluble and can be obtained from the supernatant of Bacillus cultures as described herein. These toxins have toxicity against non-mammalian pests. In a preferred embodiment, these toxins have activity against coleopteran pests. The MIS proteins are further useful due to their ability to form pores in cells. These proteins can be used with second entities including, for example, other proteins. When used with a second entity, the MIS protein will facilitate entry of the second agent into a target cell. In a preferred embodiment, the MIS protein interacts with MIS receptors in a target cell and causes pore formation in the target cell. The second entity may be a toxin or another molecule whose entry into the cell is desired.
The subject invention further concerns a family of toxins designated WAR-type toxins. The WAR toxins typically have a size of about 30-50 kDa and, most typically, have a size of about 40 kDa. Typically, these toxins are soluble and can be obtained from the supernatant of Bacillus cultures as described herein. The WAR toxins can be identified with primers described herein as well as with antibodies.
An additional family of toxins provided according to the subject invention are the toxins designated SUP-type toxins. Typically, these toxins are soluble and can be obtained from the supernatant of Bacillus cultures as described herein. In a preferred embodiment, the SUP toxins are active against lepidopteran pests. The SUP toxins typically have a size of about 70-100 kDa and, preferably, about 80 kDa. The SUP family is exemplified herein by toxins from isolate KB59A4-6. The subject invention provides probes and primers useful for the identification of toxins and genes in the SUP family.
The subject invention also provides additional Bacillus toxins and genes, including additional MIS, WAR, and SUP toxins and genes.
Toxins in the MIS, WAR, and SUP families are all soluble and can be obtained as described herein from the supernatant of Bacillus cultures. These toxins can be used alone or in combination with other toxins to control pests. For example, toxins from the MIS families may be used in conjunction with WAR-type toxins to achieve control of pests, particularly coleopteran pests. These toxins may be used, for example, with xcex4-endotoxins which are obtained from Bacillus isolates.
Table 2 provides a summary of the novel families of toxins and genes of the subject invention. Certain MIS families are specifically exemplified herein by toxins which can be obtained from particular B.t. isolates as shown in Table 2. Genes encoding toxins in each of these families can be identified by a variety of highly specific parameters, including the ability to hybridize with the particular probes set forth in Table 2. Sequence identity in excess of about 80% with the probes set forth in Table 2 can also be used to identify the genes of the various families. Also exemplified are particular primer pairs which can be used to amplify the genes of the subject invention. A portion of a gene within the indicated families would typically be amplifiable with at least one of the enumerated primer pairs. In a preferred embodiment, the amplified portion would be of approximately the indicated fragment size. Primers shown in Table 2 consist of polynucleotide sequences which encode peptides as shown in the sequence listing attached hereto. Additional primers and probes can readily be constructed by those skilled in the art such that alternate polynucleotide sequences encoding the same amino acid sequences can be used to identify and/or characterize additional genes encoding pesticidal toxins. In a preferred embodiment, these additional toxins, and their genes, could be obtained from Bacillus isolates.
Furthermore, chimeric toxins may be used according to the subject invention. Methods have been developed for making useful chimeric toxins by combining portions of B.t. proteins. The portions which are combined need not, themselves, be pesticidal so long as the combination of portions creates a chimeric protein which is pesticidal. This can be done using restriction enzymes, as described in, for example, European Patent 0 228 838; Ge, A. Z., N. L. Shivarova, D. H. Dean (1989) Proc. Natl. Acad. Sci. USA 86:4037-4041; Ge, A. Z., D. Rivers, R. Milne, D. H. Dean (1991) J. Biol. Chem. 266:17954-17958; Schnepf, H. E., K. Tomczak, J. P. Ortega, H. R. Whiteley (1990) J. Biol. Chem. 265:20923-20930; Honee, G., D. Convents, J. Van Rie, S. Jansens, M. Peferoen, B. Visser (1991) Mol. Microbiol. 5:2799-2806. Alternatively, recombination using cellular recombination mechanisms can be used to achieve similar results. See, for example, Caramori, T., A. M. Albertini, A. Galizzi (1991) Gene 98:37-44; Widner, W. R., H. R. Whiteley (1990) J. Bacteriol. 172:2826-2832; Bosch, D., B. Schipper, H. van der Kliej, R. A. de Maagd, W. J. Stickema (1994) Biotechnology 12:915-918. A number of other methods are known in the art by which such chimeric DNAs can be made. The subject invention is meant to include chimeric proteins that utilize the novel sequences identified in the subject application.
With the teachings provided herein, one skilled in the art could readily produce and use the various toxins and polynucleotide sequences described herein.
Genes and toxins. The genes and toxins useful according to the subject invention include not only the full length sequences but also fragments of these sequences, variants, mutants, and fusion proteins which retain the characteristic pesticidal activity of the toxins specifically exemplified herein. Chimeric genes and toxins, produced by combining portions from more than one Bacillus toxin or gene, may also be utilized according to the teachings of the subject invention. As used herein, the terms xe2x80x9cvariantsxe2x80x9d or xe2x80x9cvariationsxe2x80x9d of genes refer to nucleotide sequences which encode the same toxins or which encode equivalent toxins having pesticidal activity. As used herein, the term xe2x80x9cequivalent toxinsxe2x80x9d refers to toxins having the same or essentially the same biological activity against the target pests as the exemplified toxins. For example, U.S. Pat. No. 5,605,793 describes methods for generating additional molecular diversity by using DNA reassembly after random fragmentation.
It is apparent to a person skilled in this art that genes encoding active toxins can be identified and obtained through several means. The specific genes exemplified herein may be obtained from the isolates deposited at a culture depository as described above. These genes, or portions or variants thereof, may also be constructed synthetically, for example, by use of a gene synthesizer. Variations of genes may be readily constructed using standard techniques for making point mutations. Also, fragments of these genes can be made using commercially available exonucleases or endonucleases according to standard procedures. For example, enzymes such as Bal31 or site-directed mutagenesis can be used to systematically cut off nucleotides from the ends of these genes. Also, genes which encode active fragments may be obtained using a variety of restriction enzymes. Proteases may be used to directly obtain active fragments of these toxins.
Equivalent toxins and/or genes encoding these equivalent toxins can be derived from Bacillus isolates and/or DNA libraries using the teachings provided herein. There are a number of methods for obtaining the pesticidal toxins of the instant invention. For example, antibodies to the pesticidal toxins disclosed and claimed herein can be used to identify and isolate toxins from a mixture of proteins. Specifically, antibodies may be raised to the portions of the toxins which are most constant and most distinct from other Bacillus toxins. These antibodies can then be used to specifically identify equivalent toxins with the characteristic activity by immunoprecipitation, enzyme linked immunosorbent assay (ELISA), or Western blotting. Antibodies to the toxins disclosed herein, or to equivalent toxins, or fragments of these toxins, can readily be prepared using standard procedures in this art. The genes which encode these toxins can then be obtained from the microorganism.
Fragments and equivalents which retain the pesticidal activity of the exemplified toxins are within the scope of the subject invention. Also, because of the redundancy of the genetic code, a variety of different DNA sequences can encode the amino acid sequences disclosed herein. It is well within the skill of a person trained in the art to create these alternative DNA sequences encoding the same, or essentially the same, toxins. These variant DNA sequences are within the scope of the subject invention. As used herein, reference to xe2x80x9cessentially the samexe2x80x9d sequence refers to sequences which have amino acid substitutions, deletions, additions, or insertions which do not materially affect pesticidal activity. Fragments retaining pesticidal activity are also included in this definition.
A further method for identifying the toxins and genes of the subject invention is through the use of oligonucleotide probes. These probes are detectable nucleotide sequences. Probes provide a rapid method for identifying toxin-encoding genes of the subject invention. The nucleotide segments which are used as probes according to the invention can be synthesized using a DNA synthesizer and standard procedures.
Certain toxins of the subject invention have been specifically exemplified herein. Since these toxins are merely exemplary of the toxins of the subject invention, it should be readily apparent that the subject invention comprises variant or equivalent toxins (and nucleotide sequences coding for equivalent toxins) having the same or similar pesticidal activity of the exemplified toxin. Equivalent toxins will have amino acid homology with an exemplified toxin. This amino acid identity will typically be greater than 60%, preferably be greater than 75%, more preferably greater than 80%, more preferably greater than 90%, and can be greater than 95%. These identities are as determined using standard alignment techniques. The amino acid homology will be highest in critical regions of the toxin which account for biological activity or are involved in the determination of three-dimensional configuration which ultimately is responsible for the biological activity. In this regard, certain amino acid substitutions are acceptable and can be expected if these substitutions are in regions which are not critical to activity or are conservative amino acid substitutions which do not affect the three-dimensional configuration of the molecule. For example, amino acids may be placed in the following classes: non-polar, uncharged polar, basic, and acidic. Conservative substitutions whereby an amino acid of one class is replaced with another amino acid of the same type fall within the scope of the subject invention so long as the substitution does not materially alter the biological activity of the compound. Table 3 provides a listing of examples of amino acids belonging to each class.
In some instances, non-conservative substitutions can also be made. The critical factor is that these substitutions must not significantly detract from the biological activity of the toxin.
The xcex4-endotoxins of the subject invention can also be characterized in terms of the shape and location of toxin inclusions, which are described above.
As used herein, reference to xe2x80x9cisolatedxe2x80x9d polynucleotides and/or xe2x80x9cpurifiedxe2x80x9d toxins refers to these molecules when they are not associated with the other molecules with which they would be found in nature. Thus, reference to xe2x80x9cisolated and purifiedxe2x80x9d signifies the involvement of the xe2x80x9chand of manxe2x80x9d as described herein. Chimeric toxins and genes also involve the xe2x80x9chand of man.xe2x80x9d
Recombinant hosts. The toxin-encoding genes of the subject invention can be introduced into a wide variety of microbial or plant hosts. Expression of the toxin gene results, directly or indirectly, in the production and maintenance of the pesticide. With suitable microbial hosts, e.g., Pseudomonas, the microbes can be applied to the situs of the pest, where they will proliferate and be ingested. The result is a control of the pest. Alternatively, the microbe hosting the toxin gene can be killed and treated under conditions that prolong the activity of the toxin and stabilize the cell. The treated cell, which retains the toxic activity, then can be applied to the environment of the target pest.
Where the Bacillus toxin gene is introduced via a suitable vector into a microbial host, and said host is applied to the environment in a living state, it is essential that certain host microbes be used. Microorganism hosts are selected which are known to occupy the xe2x80x9cphytospherexe2x80x9d (phylloplane, phyllosphere, rhizosphere, and/or rhizoplane) of one or more crops of interest. These microorganisms are selected so as to be capable of successfully competing in the particular environment (crop and other insect habitats) with the wild-type microorganisms, provide for stable maintenance and expression of the gene expressing the polypeptide pesticide, and, desirably, provide for improved protection of the pesticide from environmental degradation and inactivation.
A large number of microorganisms are known to inhabit the phylloplane (the surface of the plant leaves) and/or the rhizosphere (the soil surrounding plant roots) of a wide variety of important crops. These microorganisms include bacteria, algae, and fungi. Of particular interest are microorganisms, such as bacteria, e.g., genera Pseudomonas, Erwinia, Serratia, Klebsiella, Xanthomonas, Streptomyces, Rhizobium, Rhodopseudomonas, Methylophilius, Agrobacterium, Acetobacter, Lactobacillus, Arthrobacter, Azotobacter, Leuconostoc, and Alcaligenes; fungi, particularly yeast, e.g., genera Saccharomyces, Cryptococcus, Kluyveromyces, Sporobolomyces, Rhodtorula, and Aureobasidium. Of particular interest are such phytosphere bacterial species as Pseudomonas syringae, Pseudomonas fluorescens, Serratia marcescens, Acetobacter xylinum, Agrobacterium tumefaciens, Rhodopseudomonas spheroides, Xanthomonas campestris, Rhizobium melioti, Alcaligenes entrophus, and Azotobacter vinlandii; and phytosphere yeast species such as Rhodotorula rubra, R. glutinis, R. marina, R. aurantiaca, Cryptococcus albidus, C. diffluens, C. laurentii, Saccharomyces rosei, S. pretoriensis, S. cerevisiae, Sporobolomyces roseus, S. dorus, Kluyveromyces veronae, and Aureobasidium pollulans. Of particular interest are the pigmented microorganisms.
A wide variety of ways are available for introducing a Bacillus gene encoding a toxin into a microorganism host under conditions which allow for stable maintenance and expression of the gene. These methods are well known to those skilled in the art and are described, for example, in U.S. Pat. No. 5,135,867, which is incorporated herein by reference.
Synthetic genes which are functionally equivalent to the toxins of the subject invention can also be used to transform hosts. Methods for the production of synthetic genes can be found in, for example, U.S. Pat. No. 5,380,831.
Treatment of cells. As mentioned above, Bacillus or recombinant cells expressing a Bacillus toxin can be treated to prolong the toxin activity and stabilize the cell. The pesticide microcapsule that is formed comprises the Bacillus toxin within a cellular structure that has been stabilized and will protect the toxin when the microcapsule is applied to the environment of the target pest. Suitable host cells may include either prokaryotes or eukaryotes. As hosts, of particular interest will be the prokaryotes and the lower eukaryotes, such as fungi. The cell will usually be intact and be substantially in the proliferative form when treated, rather than in a spore form.
Treatment of the microbial cell, e.g., a microbe containing the Bacillus toxin gene, can be by chemical or physical means, or by a combination of chemical and/or physical means, so long as the technique does not deleteriously affect the properties of the toxin, nor diminish the cellular capability of protecting the toxin. Methods for treatment of microbial cells are disclosed in U.S. Pat. Nos. 4,695,455 and 4,695,462, which are incorporated herein by reference.
Methods and formulations for control of pests. Control of pests using the isolates, toxins, and genes of the subject invention can be accomplished by a variety of methods known to those skilled in the art. These methods include, for example, the application of Bacillus isolates to the pests (or their location), the application of recombinant microbes to the pests (or their locations), and the transformation of plants with genes which encode the pesticidal toxins of the subject invention. Transformations can be made by those skilled in the art using standard techniques. Materials necessary for these transformations are disclosed herein or are otherwise readily available to the skilled artisan.
Formulated bait granules containing an attractant and the toxins of the Bacillus isolates, or recombinant microbes comprising the genes obtainable from the Bacillus isolates disclosed herein, can be applied to the soil. Formulated product can also be applied as a seed-coating or root treatment or total plant treatment at later stages of the crop cycle. Plant and soil treatments of Bacillus cells may be employed as wettable powders, granules or dusts, by mixing with various inert materials, such as inorganic minerals (phyllosilicates, carbonates, sulfates, phosphates, and the like) or botanical materials (powdered corncobs, rice hulls, walnut shells, and the like). The formulations may include spreader-sticker adjuvants, stabilizing agents, other pesticidal additives, or surfactants. Liquid formulations may be aqueous-based or non-aqueous and employed as foams, gels, suspensions, emulsifiable concentrates, or the like. The ingredients may include rheological agents, surfactants, emulsifiers, dispersants, or polymers.
As would be appreciated by a person skilled in the art, the pesticidal concentration will vary widely depending upon the nature of the particular formulation, particularly whether it is a concentrate or to be used directly. The pesticide will be present in at least 1% by weight and may be 100% by weight. The dry formulations will have from about 1-95% by weight of the pesticide while the liquid formulations will generally be from about 1-60% by weight of the solids in the liquid phase. The formulations that contain cells will generally have from about 102 to about 104 cells/mg. These formulations will be administered at about 50 mg (liquid or dry) to 1 kg or more per hectare.
The formulations can be applied to the environment of the pest, e.g., soil and foliage, by spraying, dusting, sprinkling, or the like.
Polynucleotide probes. It is well known that DNA possesses a fundamental property called base complementarity. In nature, DNA ordinarily exists in the form of pairs of anti-parallel strands, the bases on each strand projecting from that strand toward the opposite strand. The base adenine (A) on one strand will always be opposed to the base thymine (T) on the other strand, and the base guanine (G) will be opposed to the base cytosine (C). The bases are held in apposition by their ability to hydrogen bond in this specific way. Though each individual bond is relatively weak, the net effect of many adjacent hydrogen bonded bases, together with base stacking effects, is a stable joining of the two complementary strands. These bonds can be broken by treatments such as high pH or high temperature, and these conditions result in the dissociation, or xe2x80x9cdenaturation,xe2x80x9d of the two strands. If the DNA is then placed in conditions which make hydrogen bonding of the bases thermodynamically favorable, the DNA strands will anneal, or xe2x80x9chybridize,xe2x80x9d and reform the original double stranded DNA. If carried out under appropriate conditions, this hybridization can be highly specific. That is, only strands with a high degree of base complementarity will be able to form stable double stranded structures. The relationship of the specificity of hybridization to reaction conditions is well known. Thus, hybridization may be used to test whether two pieces of DNA are complementary in their base sequences. It is this hybridization mechanism which facilitates the use of probes of the subject invention to readily detect and characterize DNA sequences of interest.
The probes may be RNA, DNA, or PNA (peptide nucleic acid). The probe will normally have at least about 10 bases, more usually at least about 17 bases, and may have up to about 100 bases or more. Longer probes can readily be utilized, and such probes can be, for example, several kilobases in length. The probe sequence is designed to be at least substantially complementary to a portion of a gene encoding a toxin of interest. The probe need not have perfect complementarity to the sequence to which it hybridizes. The probes may be labelled utilizing techniques which are well known to those skilled in this art.
One approach for the use of the subject invention as probes entails first identifying by Southern blot analysis of a gene bank of the Bacillus isolate all DNA segments homologous with the disclosed nucleotide sequences. Thus, it is possible, without the aid of biological analysis, to know in advance the probable activity of many new Bacillus isolates, and of the individual gene products expressed by a given Bacillus isolate. Such a probe analysis provides a rapid method for identifying potentially commercially valuable insecticidal toxin genes within the multifarious subspecies of B.t.
One hybridization procedure useful according to the subject invention typically includes the initial steps of isolating the DNA sample of interest and purifying it chemically. Either lysed bacteria or total fractionated nucleic acid isolated from bacteria can be used. Cells can be treated using known techniques to liberate their DNA (and/or RNA). The DNA sample can be cut into pieces with an appropriate restriction enzyme. The pieces can be separated by size through electrophoresis in a gel, usually agarose or acrylamide. The pieces of interest can be transferred to an immobilizing membrane.
The particular hybridization technique is not essential to the subject invention. As improvements are made in hybridization techniques, they can be readily applied.
The probe and sample can then be combined in a hybridization buffer solution and held at an appropriate temperature until annealing occurs. Thereafter, the membrane is washed free of extraneous materials, leaving the sample and bound probe molecules typically detected and quantified by autoradiography and/or liquid scintillation counting. As is well known in the art, if the probe molecule and nucleic acid sample hybridize by forming a strong non-covalent bond between the two molecules, it can be reasonably assumed that the probe and sample are essentially identical. The probe""s detectable label provides a means for determining in a known manner whether hybridization has occurred.
In the use of the nucleotide segments as probes, the particular probe is labeled with any suitable label known to those skilled in the art, including radioactive and non-radioactive labels. Typical radioactive labels include 32P, 35S, or the like. Non-radioactive labels include, for example, ligands such as biotin or thyroxine, as well as enzymes such as hydrolases or perixodases, or the various chemilurninescers such as luciferin, or fluorescent compounds like fluorescein and its derivatives. The probes may be made inherently fluorescent as described in International Application No. WO 93/16094.
Various degrees of stringency of hybridization can be employed. The more severe the conditions, the greater the complementarity that is required for duplex formation. Severity can be controlled by temperature, probe concentration, probe length, ionic strength, time, and the like. Preferably, hybridization is conducted under moderate to high stringency conditions by techniques well known in the art, as described, for example, in Keller, G. H., M. M. Manak (1987) DNA Probes, Stockton Press, New York, N.Y., pp. 169-170.
As used herein xe2x80x9cmoderate to high stringencyxe2x80x9d conditions for hybridization refers to conditions which achieve the same, or about the same, degree of specificity of hybridization as the conditions employed by the current applicants. Examples of moderate and high stringency conditions are provided herein. Specifically, hybridization of immobilized DNA on Southern blots with 32P-labeled gene-specific probes was performed by standard methods (Maniatis et al.). In general, hybridization and subsequent washes were carried out under moderate to high stringency conditions that allowed for detection of target sequences with homology to the exemplified toxin genes. For double-stranded DNA gene probes, hybridization was carried out overnight at 20-25xc2x0 C. below the melting temperature (Tm) of the DNA hybrid in 6xc3x97SSPE, 5xc3x97Denhardt""s solution, 0.1% SDS, 0.1 mg/ml denatured DNA. The melting temperature is described by the following formula (Beltz, G. A., K. A. Jacobs, T. H. Eickbush, P. T. Cherbas, and F. C. Kafatos [1983] Methods of Enzymology, R. Wu, L. Grossman and K. Moldave [eds.] Academic Press, New York 100:266-285).
Tm=81.5xc2x0 C.+16.6 Log[Na+]+0.41(%G+C)xe2x88x920.61(%formamide)xe2x88x92600/length of duplex in base pairs.
Washes are typically carried out as follows:
(1) Twice at room temperature for 15 minutes in 1xc3x97SSPE, 0.1% SDS (low stringency wash).
(2) Once at Tmxe2x88x9220xc2x0 C. for 15 minutes in 0.2xc3x97SSPE, 0.1% SDS (moderate stringency wash).
For oligonucleotide probes, hybridization was carried out overnight at 10-20xc2x0 C. below the melting temperature (Tm) of the hybrid in 6xc3x97SSPE, 5xc3x97Denhardt""s solution, 0.1% SDS, 0.1 mg/ml denatured DNA. Tm for oligonucleotide probes was determined by the following formula:
Tm (xc2x0 C.)=2(number T/A base pairs)+4(number G/C base pairs) (Suggs, S. V., T. Miyake, E. H. Kawashime, M. J. Johnson, K. Itakura, and R. B. Wallace [1981] ICN-UCLA Symp. Dev. Biol. Using Purified Genes, D. D. Brown [ed.], Academic Press, New York, 23:683-693).
Washes were typically carried out as follows:
(1) Twice at room temperature for 15 minutes 1xc3x97SSPE, 0.1% SDS (low stringency wash).
(2) Once at the hybridization temperature for 15 minutes in 1xc3x97SSPE, 0.1% SDS (moderate stringency wash).
In general, salt and/or temperature can be altered to change stringency. With a labeled DNA fragment greater than 70 or so bases in length, the following conditions can be used:
Low: 1 or 2xc3x97SSPE, room temperature
Low: 1 or 2xc3x97SSPE, 42xc2x0 C.
Moderate: 0.2xc3x97 or 1xc3x97SSPE, 65xc2x0 C.
High: 0.1xc3x97SSPE, 65xc2x0 C.
Duplex formation and stability depend on substantial complementarity between the two strands of a hybrid, and, as noted above, a certain degree of mismatch can be tolerated. Therefore, the probe sequences of the subject invention include mutations (both single and multiple), deletions, insertions of the described sequences, and combinations thereof, wherein said mutations, insertions and deletions permit formation of stable hybrids with the target polynucleotide of interest. Mutations, insertions, and deletions can be produced in a given polynucleotide sequence in many ways, and these methods are known to an ordinarily skilled artisan. Other methods may become known in the future.
Thus, mutational, insertional, and deletional variants of the disclosed nucleotide sequences can be readily prepared by methods which are well known to those skilled in the art. These variants can be used in the same manner as the exemplified primer sequences so long as the variants have substantial sequence homology with the original sequence. As used herein, substantial sequence homology refers to homology which is sufficient to enable the variant probe to function in the same capacity as the original probe. Preferably, this homology is greater than 50%; more preferably, this homology is greater than 75%; and most preferably, this homology is greater than 90%. The degree of homology needed for the variant to function in its intended capacity will depend upon the intended use of the sequence. It is well within the skill of a person trained in this art to make mutational, insertional, and deletional mutations which are designed to improve the function of the sequence or otherwise provide a methodological advantage.
PCR technology. Polymerase Chain Reaction (PCR) is a repetitive, enzymatic, primed synthesis of a nucleic acid sequence. This procedure is well known and commonly used by those skilled in this art (see Mullis, U.S. Pat. Nos. 4,683,195, 4,683,202, and 4,800,159; Saiki, Randall K., Stephen Scharf, Fred Faloona, Kary B. Mullis, Glenn T. Horn, Henry A. Erlich, Norman Arnheim [1985] xe2x80x9cEnzymatic Amplification of xcex2-Globin Genomic Sequences and Restriction Site Analysis for Diagnosis of Sickle Cell Anemia,xe2x80x9d Science 230:1350-1354.). PCR is based on the enzymatic amplification of a DNA fragment of interest that is flanked by two oligonucleotide primers that hybridize to opposite strands of the target sequence. The primers are oriented with the 3xe2x80x2 ends pointing towards each other. Repeated cycles of heat denaturation of the template, annealing of the primers to their complementary sequences, and extension of the annealed primers with a DNA polymerase result in the amplification of the segment defined by the 5xe2x80x2 ends of the PCR primers. Since the extension product of each primer can serve as a template for the other primer, each cycle essentially doubles the amount of DNA fragment produced in the previous cycle. This results in the exponential accumulation of the specific target fragment, up to several million-fold in a few hours. By using a thermostable DNA polymerase such as Taq polymerase, which is isolated from the thermophilic bacterium Thermus aquaticus, the amplification process can be completely automated. Other enzymes which can be used are known to those skilled in the art.
The DNA sequences of the subject invention can be used as primers for PCR amplification. In performing PCR amplification, a certain degree of mismatch can be tolerated between primer and template. Therefore, mutations, deletions, and insertions (especially additions of nucleotides to the 5xe2x80x2 end) of the exemplified primers fall within the scope of the subject invention. Mutations, insertions and deletions can be produced in a given primer by methods known to an ordinarily skilled artisan.
All of the references cited herein are hereby incorporated by reference.